Diferent multicast addresses for a storage group



  • Hi,
    we know that in order to make multicast deployments Fog uses udp-sender which in default uses a multicast address based on host IP. As you sure know that makes only one multicast deployment possible at once.
    Is there an easy way to change that and allow multiple multicast deployments in a single storage repository or do you have plans to change that in future versions?

    Thanks and regards.

    Frank



  • Thanks Tom. I didn’t pretend to criticized Fog in any way because I think it is a great tool and there is an excellent work behind it.
    We think that multicast is a very good way to get the best from network bandwidth if you are sending the same image to multiple clients, so we think that a product like fog could take profit of this.
    From you answer I guess that multicast is not a priority so I will follow your advise and I will try to modify code to allow multiple multicast transfers. The only thing I wanted to know it was if that was in your roadmap.

    Thanks a lot anyway.

    Frank


  • Senior Developer

    I’m not trying to say you haven’t done your own research. In Fact, I am certain you are correct. But it’s not a road I’m willing to go down. If you want to change the IP’s and configs to do such a thing, be my guest. I prefer not using Multicast and have very limited experience even when using it.



  • What I can tell you it’s that we have been fighting with multicast transfers for log time ago with several deployment systems as rembo an Tivoli later, so we have some experience on that. I’m not an expert with network, but we have a network team group here with great experience and we have been working closely with them.

    It’s true that for multicast as for unicast there is an IP and a port, but what makes possible different multicast transfers is what is called a multicast group, and that depends only on IP as I said. If you monitor multicast info in switches you can notice that. Also note that neither udp-sender manual page nor the wiki page you told me don’t talk about multicast port settings but only IP settings. So one multicast address mean only one multicast group and that’s why I posted my question.

    Check that if you want to in a test environment and you will see that only one multicast group is created for all the multicasts transfers, which of course makes that all hosts in the group receive packets from all multicasts transfers.

    Frank


  • Senior Developer

    I’m no guru on multicast myself. That said, isn’t multicast port driven? While you can specify different multicast IP’s and it may help in cases where people have multiple nic’s to give up, it’s ultimately dependent on the port to know where to get the data from. At least from the client side. The only people who care about the data are the one’s listening for that port.

    I am under the impression, that while the multicast IP can be changed, it’s usually set for 224.0.0.X range. Source specific is generally in the 232.0.0.X range and SSDP is done on 239.255.255.250

    A good read:
    http://en.wikipedia.org/wiki/Multicast_address

    At any rate it’s standard, but not necessarily something people must follow. In their own environments they may want to use other custom addresses for handling this, but this is NOT the norm. The Ports that are sending AND/OR listening are the important parts, otherwise a single multicast system would DESTROY a network.



  • Hi Tom,
    I’m not a guru of multicast, but I am quite sure that multicast groups depend only on multicas IP not port. In fact, in udp-sender there is no option for multicast port, only for unicast.

    So I don’t see that different multicasts deployment perform well if you don’t change multicast IP. Of course you can launch several multicast deployments, but all of them will be on the same multicast group, which leads to a poor network performance.

    Frank


  • Senior Developer

    You can have multiple multicast deployments at once from a single FOG Server. If you were trying to use the same port you’d be running into issues, but as I randomize the port so this doesn’t happen you shouldn’t have any issues.


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